Mobile traffic demand has been growing substantially in recent years. To meet this growing demand for streaming, gaming, social networking and other multimedia services in parallel with the voice communication, 3GPP formulated Long Term Evolution (LTE) providing enhanced user experience. The LTE technology enables deployment of femtocells also called Home Evolved Node Bs (HeNBs) delivering low power, high-performance access to a user. Usually deployed in homes and businesses, a femtocell can cover hotspots. The user receiving mobile services from a network operator can switch his/her User Equipment (UE) to any of these available femtocells in the vicinity. The UE's access to the femtocell can be restricted through formation of a Closed Subscriber Group (CSG), where each femtocell providing restricted access is member of one or more CSG cells. The UE identifies allowed CSG cells using CSG Identifiers (IDs) specified in the UE's Operator CSG (OCSG) list and Allowed CSG (ACSG) list provided in a Universal Subscriber Identity Module (USIM). The UE selects a CSG cell either using automatic CSG selection mode or manual CSG selection mode. The manual selection mode is a popular choice for the CSG cell selection whenever user desires to choose a CSG cell based on his/her current requirements. Thus the mobile traffic growth, driven by new services and UE capabilities, is paralleled by user expectations. The network operators aim to provide best possible connectivity to the user while user moves through heterogeneous network comprising macro cells, pico cells and femtocells.
While in manual CSG selection mode the UE may switch in and out of the CSG cell, hop between the CSG cells within and outside UE's Registered Public Land Mobile Network (RPLMN). Whenever the UE leaves the currently registered CSG cell, the UE may find itself in coverage area of one or more PLMN operators such as UE's Home Operator (Home Public Mobile Network (HPLMN)), other network operators including Visitors PLMN (VPLMN) and Equivalent PLMN (EPLMN). The RPLMN is the PLMN on which the UE has performed a location registration successfully. The HPLMN is the PLMN in which the UE holds its subscription. The EPLMNs contained in the list of equivalent PLMNs in the UE are PLMNs that are considered equivalent to the HPLMN for PLMN selection, cell selection, cell re-selection and handover. The VPLMN is PLMN that generally offers only limited services such as emergency call only to the UE, except in certain cases such as roaming services if activated by the UE. To provide enhanced user experience during the manual CSG selection mode the UE should be able to recover back to the normal service at earliest in case registration attempt to the CSG cell fails or UE experiences loss of CSG coverage.
In accordance with existing methods defined in current 3GPP specification for the UE behavior in CSG manual selection mode, the UE scans available CSG cells and displays them to the user based on configuration by the HPLMN on a Universal Integrated Circuit Card (UICC). Upon manual selection of the CSG cell by the user, the UE behavior is differentiated based on whether a selected CSG cell belongs to the UE's RPLMN or not. If the PLMN of the selected CSG cell is different than the currently registered PLMN, then the UE saves PLMN selection mode associated with the RPLMN and duplicates value of RPLMN into a non-volatile memory. For any further hops to different CSG associated with other PLMNs, the UE retains the saved duplicate value of RPLMN, however, updates the stored PLMN selection mode in accordance with the most recent PLMN selection mode. Upon, loss of coverage on the user selected CSG cell, the UE changes the current PLMN selection mode to the stored duplicate PLMN selection mode and attempts normal service recovery with the stored duplicate value of RPLMN. In a scenario where the UE in the RPLMN with automatic PLMN selection mode hops across multiple CSG cells before attempting to recover normal service as result of loss of CSG cell coverage, detects the stored duplicate PLMN selection mode to be manual. Thus, updating of PLMN selection mode during every hop from one CSG cell to another in manual CSG selection mode changes the stored PLMN selection mode to manual. This prevents the UE to automatically recover to the normal service on using the stored duplicate value of RPLMN and requires user intervention to select the PLMN manually. This delay may force the UE to enter limited service area of the wireless network.
In another scenario, when the UE in manual PLMN selection mode receives a attach reject with any reject cause such as reject cause #35 (indicating the UE to delete the EPLMN list) during attempt of registration on the selected CSG cell, the UE deletes the stored EPLMN list. This creates an issue while the UE attempts to recover to normal service on loss of coverage of the selected CSG cell as well as loss of coverage of the RPLMN. Thus, with no EPLMN list the UE is forced into limited service even though coverage from an EPLMN is available.
Moreover, the current 3GPP specification does not define actions to be taken by the UE after a HPLMN timer expiry when the UE is in manual CSG selection mode registered with the selected CSG cell associated with the RPLM and is in automatic PLMN selection mode. The existing 3GPP specification also does not state the UE behavior when the user changes the PLMN Selection mode to automatic when CSG selection mode is manual.
In the existing method the UE behavior is defined to update ACSG list whenever registration on the selected CSG cell in manual CSG selection mode is successful. However, irrespective of whether the CSG ID of the registered CSG cell exists in the OCSG list the current 3GPP specification duplicates the CSG ID in the ACSG list. This reduces number of valid CSG ID entries possible in the UE's ACSG list.
The principal object of the embodiments herein is to provide a method and system enabling a User Equipment (UE) to quickly recover back to normal service on failure of registration attempt to a selected Closed Subscriber Group (CSG) or on experiencing loss of coverage of the selected CSG cell when the UE is in a manual CSG selection mode and the selected CSG cell is associated with a different Public Land Mobile Network (PLMN) than the Registered PLMN (RPLMN) of the UE.
Another object of the embodiments herein is to provide a method for handling request to change a current Public Land Mobile Network (PLMN) selection mode in the UE, when the UE is attached to the selected CSG cell in the manual CSG selection mode.
Another object of the embodiments herein is to provide a method for handling expiry of a Home PLMN (HPLMN) timer in the UE in the manual CSG selection mode, when the UE is attached to the selected CSG cell associated with the RPLMN of the UE and the RPLMN of the UE is different from the HPLMN of the UE.